1. Field of the Invention
The invention relates to a process for making baked articles from grain products using enzymes, with the objective of preventing staling of the baked articles.
2. Description of the Background
Prevention of staling or, stated positively, retention of freshness of baked articles has been a problem as long as bread has been baked. Heretofore the sales outlets for baked articles, the bakeries and even the consumers have made the best of the situation and become accustomed to the fact that rolls, for example, must be sold and eaten on the same day. Prolonging the freshness by several days would be desirable and would decisively change consumer behavior and the distribution strategy for this important basic food. In the course of the wave of innovations in food technology in recent years, enzyme technology has confronted this problem and already suggested several solutions.
The staling process is extremely complex and in no case is completely understood. Even the manifestation of the effect is multi-faceted. The following adverse phenomena are observed:
1. An increase in firmness of the crumb. The bread becomes hard. PA0 2. The bread crust becomes leathery or rubbery. PA0 3. Loss of bread aroma. An unpleasant odor characteristic can even develop. PA0 1. High enzyme dosages must not be needed to achieve the effect PA0 2. The enzyme addition must be dosage-tolerant PA0 3. The enzyme must be completely deactivated after the baking process PA0 4. The cleavage products must cause the least possible change in flavor, and in particular they must not consist exclusively of sugar. PA0 5. The bread aroma must be preserved as much as possible.
The experts unanimously believe that staling of baked articles is related to retrogradation of the starch and to the associated change in water-retention capacity. Starch is an essential constituent of baked articles, and is present in dough in the form of particles coated with protein. During the baking process the starch becomes gelatinized and absorbs copious water, while the protein coagulates. Immediately after baking the starch begins to recrystallize (=retrograde) and release water. The firmness of the crumb increases, although this is still regarded as an advantage in the first four hours. The sliceability and chewing characteristics improve at first. It is assumed that the unbranched starch fraction, or the amylose, crystallizes first, followed by the branched fraction of the starch, or the amylopectin, during further storage. In the meantime the crumb becomes stiffer and in the course of time increasingly less elastic and eventually dry and hard: the bread has become stale.
In contrast, the crust loses crispness during storage. It is assumed that water is released by recrystallization, diffuses outward from the crumb and moistens the crust completely through. As a result, the crust becomes tough and leathery. Among the possible reasons for the loss of aroma of stale bread may be inclusion of the aroma substances in the starch helix.
It is undisputed that the causal key reaction for all of these staling phenomena is starch retrogradation. Suppressing or circumventing this phenomenon is the subject matter of numerous protective rights and publications.
One strategy for hindering at least partly the considerable firming of the crumb during storage has already been long known: the crumb is made in softer form from the beginning. The means of choice are emulsifiers such as lecithin, lysolethicin, diacetyltartaric acid esters or monoglyceride and diglyceride esters, which are added to the dough and produce crumb structure which is particularly soft from the beginning. It is also postulated that the monoglyceride and diglyceride esters on the one hand absorb the water released by recrystallization and on the other hand associate with the amylose, thus interfering with recrystallization thereof to the point that it can no longer proceed to completion. The use of alpha-amylase derived from fungi such as Aspergillus oryzae also has a similar effect. It acts upon damaged starch particles, thereby lowering the viscosity of the dough and producing fermentable sugar. As a consequence, the finished baked article has larger volume, which is consistent with softer crumb: The process of firming during aging is not as pronounced when the crumb is particularly soft.
Aside from the fact that the fresh bread is too soft, this strategy does not prevent or inadequately prevents the development of a rubbery consistency of the crumb as well as the other flaws of bread when it becomes stale.
A further strategy, specifically that of preventing retrogradation by partly enzyme-mediated hydrolysis of the two starch fractions, is therefore more promising. It is assumed that the fragments produced by hydrolysis of the starch are too short to be able to recrystallize. The fragments associate with the remaining high molecular weight starch and largely prevent recrystallization thereof as well. In the experts' view, enzyme-mediated hydrolysis of the crumb should take place if possible at the gelatinization temperature, or in other words above about 70.degree. C. These temperatures are reached and exceeded without difficulty in the baking process. The dilemma of enzyme treatment, however, is that only partial hydrolysis is permissible: not too little and not too much. If the degree of hydrolysis is too low, the freshness will not be retained. This is the case, for example, if starch-cleaving enzymes with too low thermal stability are used, such as the above-mentioned alpha-amylase derived from fungi. Such an enzyme has already lost its activity if gelatinization begins in the course of the thermal stress during the baking process, with the result that hydrolysis of the starch is too little.
The use of alpha-amylases derived from bacteria such as Bacillus subtilis or Bacillus stearothermophilus leads to high degrees of hydrolysis. Because these are extremely thermally stable they are hardly deactivated during the baking process and even act subsequently during the cooling process. The consequence is excessive breakdown of the starch, leading to moist, sticky crumb. It is difficult to control the desired partial hydrolysis of the starch merely by accurate dosage of this enzyme.
The object therefore exists to break down the starch only to a specified degree of hydrolysis, with the proviso of adequate dosage tolerance for the added enzyme.
In U.S. Pat. No. 4,416,903 it is proposed that the known alpha-amylase derived from fungi be made usable for the purposes of freshness retention by embedding in a sugary medium having a stabilizing effect against thermal stress. The process does not work without added emulsifier and sugar, and it cannot be used for numerous baked articles in which added sugar is undesirable.
PCT application WO 89/08403 also relates to the use of alpha-amylase derived from fungi for keeping bread fresh. Therein there is proposed the use of an acid-stable alpha-amylase derived from fungi which, even at the elevated temperatures of the baking process, is still sufficiently active, or in other words cleaves starch up to a specified degree of hydrolysis, in the slightly acid medium of the dough. The enzyme is isolated from black-spored Aspergillus strains and has a pH optimum of 3 to 5 at 60 to 70.degree. C. In general, relatively high enzyme dosages must be added to achieve an effect in the uses of alpha-amylases derived from fungi described hereinabove.
U.S. Pat. No. 4,654,216 attempts to solve the problem of keeping bread fresh by means of special specificity of the enzyme used. It relates to a pullulanase, which is used together with amylase derived from bacteria or from malt. Supposedly it cleaves mainly the branched amylopectin and thus supports the action of the amylases. Since the enzymes used are thermally stable, the problem that the enzyme must be added with pinpoint accuracy persists here, and must lead to difficulties in practice.
Another method which is also based on the specificity of the enzyme used is claimed in PCT Application WO 91/04669. Therein maltogenic exoamylases, otherwise known as beta-amylases, are proposed for prevention of staling. This enzyme species cleaves exclusively maltose from starch molecules. Two different beta-amylases derived from bacilli are cited. Their source and preparation are described in European Patent 234858 and U.S. Pat. No. 4,604,355.
Since these enzymes are highly thermally stable--both enzymes still retain more than 50% of their activity after 30 minutes of thermal stress at 80.degree. C.--it can be assumed that their action is not limited in the course of time, or in other words that they act throughout the entire baking process and thereafter. Consequently, at least part of the enzymes must survive the baking process and thus still be present in active condition even in the finished baked article. One of the doctrines of food technology is that if enzymes are present in ready-to-eat products they should be in inactivated condition, which is not assured with certainty in this case and is a disadvantage. The action of these enzymes supposedly comprises quantitatively limited cleavage into lower molecular weight fragments, which improve water-retention capability and simultaneously prevent recrystallization of the residual starch. The reaction goes as far as beta residual dextrin, where it stops. Another disadvantage is that the cleavage products are exclusively sugars, which is undesirable in some cases for flavor reasons.
Thermally stable exoglucanases such as beta-amylases or amyloglucosidases are also proposed in European Patent 412607 for prevention of staling. They can be supplemented or replaced by alpha-1,6-endoglucanases such as pullulanase. Here also the enzymes are active during baking between 80 and 95.degree. C., and their complete inactivation at the end of the baking process is not assured with certainty. Supposedly the amylopectin components in particular are selectively hydrolyzed by the choice of these specificities, and the reaction can also go beyond residual dextrin. Thus the problem of adding enzyme with pinpoint accuracy is also present here.